1. Field of Invention
The invention relates to devices for measuring crystal orientation and crystal distortion in polycrystalline materials.
2. Description of Related Art
The Laue X-ray method has conventionally been used to measure the crystal orientation of metallic materials, ceramics, rocks and the like. In addition, the Kossel X-rays method has commonly been used to measure distortion introduced in crystals (hereinafter referred to as xe2x80x9ccrystal distortionxe2x80x9d). These methods, however, disadvantageously target crystal grains on the order of several millimeters or larger, and they are not applicable to minute crystal grains on the order of 5 to 20 xcexcm, which constitute common metallic materials.
Accordingly, the crystal orientation of such minute crystal grains has typically been measured and analyzed as a formation texture, by using, for example, polar diagrams. This approach, however, only determines the average crystal orientation of a large number of crystal grains. Thus, this approach did not substantially contribute to research and development in the field of secondary recrystallization. In secondary recrystallization, detailed information is required for each crystal grain, not information on averages, because only one out of every two million crystal grains becomes the nucleus for secondary crystallization.
In the 1970s, the Kossel X-rays transmission method, the Kossel X-rays reflection method, and the electron channeling pattern method (also referred to as the Kikuchi line method), which all employ electron beams, were developed as alternatives to the Laue X-rays method and the Kossel X-rays method. These newly developed methods enabled detection of crystal orientation and crystal distortion in minute crystal grains on the order of 5 to 20 xcexcm.
Furthermore, the development of computers and image analysis techniques enabled automated analysis of crystal orientation and crystal distortion for large numbers of minute crystal grains. The mapping of the analysis results allowed further analysis on nucleation and selective growth of the crystal grains, and colored mapping S allowed visualization of the generation and distribution of complex crystal grains composed of two or more elements. These features are disclosed in Japanese Patent Publications Nos. Hei 7-9564 and Hei 6-86141.
In the Kossel X-rays reflection method, a focused electron beam is emitted onto a bulk sample, Kossel X-rays generated within a pyriform area from approximately a depth of 0.5 xcexcm in the bulk sample are detected, and crystal orientation and crystal distortion in the bulk sample are calculated based on the diffraction pattern. The details of the Kossel X-rays reflection method are described in xe2x80x9cA New Method for Local Crystal Orientation Analysisxe2x80x9d (Yoshimitsu Iwasaki et al., Proceedings of the Japanese Metal Society Meeting, 18, 1979, p. 632)
Kossel X-rays are formed by weak divergent X-rays caused by irradiating crystal grains with an electron beam or X-rays, characteristic X-rays thereby being generated in the bulk sample. In the Kossel X-rays reflection method, however, continuous X-rays, reflected electron beams, and secondary electron beams are generated together with the Kossel X-rays, making it very difficult to extract the Kossel X-rays.
Japanese Patent Publication No. Hei 6-22108 proposes a particular type of thin-film filter disposed between a bulk sample and a Kossel X-rays detector. The filter is an iron thin film on which one of Fe, Mn, Cr, V, Ti and the like is deposited.
Japanese Unexamined Patent Application Publication No. Hei 10-68703 proposes a filter composed of beryllium, disposed in front of a Kossel X-rays detector in order to more effectively reduce negative effects of visible light and undesirable electron beams.
FIG. 1 shows an exemplary Kossel X-rays reflection device. As shown, the device structure and operation includes a focused electron beam 1, reflected electron beams and X-rays 1xe2x80x2, a bulk sample 2, a sample holder 20, a filter 3 composed of beryllium, Kossel X-rays 1xe2x80x3, a phosphor 4 composed of a phosphorous compound, glass fibers 5 (the phosphor 4 and the glass fibers 5 constituting a phosphor unit 6), a detector 7 implemented by a CCD camera, an image processing unit 8, a display unit 9 (the image processing unit 8 and the display unit 9 constituting an image analysis device 10), and a filter 11 composed of iron.
In order to obtain Kossel X-rays of sufficient intensity, the focused electron beam current is usually about several microamperes. In addition, in order to enhance the accuracy of Kossel X-rays detection and also to minimize effects of background radiation, the gap between the bulk sample 2 and the detector 7 is determined in accordance with the electron beam current. The distance between the bulk sample 2 and the beryllium filter 3 may be varied from approximately 9 to 15 cm. The Kossel X-rays reflection device is disadvantageously larger than the electron beam diffraction device primarily due to this gap. Another disadvantage of the Kossel X-rays reflection device is that, because it must detect weak X-rays, it takes about 40 seconds on average to measure one crystal grain.
Another method of analyzing crystal orientation and crystal distortion of minute crystal grains is the electron beam diffraction method such as, for example, the electron channeling pattern (ECP) method using the Kikuchi pattern. The details of the method are described in xe2x80x9cMaterial Characteristics and Control of Crystal Orientation Distribution in Polycrystalline Materialsxe2x80x9d (Youichi Ishida, Japanese Metal Society Seminar, July 1992, pp. 7-12).
Recently, it has been reported that TexSEM Laboratories, Inc. of the United States has developed an electron beam diffraction technique that employs electron back-scatter diffraction, a modification of the method based on the Kikuchi pattern, to measure and analyze crystal orientation of minute crystal grains in a very short time. It has also been reported that Oxford, Inc. of the United Kingdom and Noran Instruments, Inc. of the United States have also developed similar devices, which are sold as TexSEM Laboratories, Inc.
The electron beam diffraction method has the following features.
(1) The capability of measurement of small areas on the order of 0.2 xcexcm due to the use of extremely narrow electron beams with high voltage and small current (on the order of several nanoamperes).
(2) The capability of measurements in the superficial layer on the order of 0.05 xcexcm or less in depth.
(3) A high accuracy of xc2x11xc2x0 in crystal orientation analysis can be achieved.
(4) Automated analysis that allows rapid measurement of approximately 0.3 to 1.5 seconds for each measured area, and the display of a polar diagram. Usually, more than ten thousands areas can be measured in a few hours.
Because the electron beam current is small, the gap between a sample and the detector can also be made small. Therefore, the electron beam diffraction device can be made more compact than can the Kossel X-rays device.
However, because electron beams penetrate no deeper than the shallow surface, the following problems arise.
(a) In preparing a sample, the sample surface must be treated with special care in order to prevent oxidation and distortion of the surface.
(b) It is not possible to obtain information concerning inner portions just below the shallow surface.
(c) Crystal distortion data is less accurate than in the Kossel X-rays reflection method.
As described above, the Kossel X-rays reflection method and the electron beam diffraction method both have their respective advantages and disadvantages. Each of these methods is unable to achieve quick and accurate measurement of both crystal orientation and crystal distortion.
Accordingly, it is an object of this invention to provide a compact device for measuring crystal orientation and crystal distortion in polycrystalline materials, in which measurement time is reduced and measurement accuracy is enhanced.
To achieve this object, this invention provides a device for measuring crystal orientation and crystal distortion in polycrystalline materials. The device includes a focused electron beam generator, a sample holder, an electron beam detector, a Kossel X-rays detector, an image processor and a display. Preferably, the electron beam detector includes an electron beam receiving surface, a phosphor element and a detector. The Kossel X-rays detector preferably includes a Kossel X-rays receiving surface, a phosphor element and a detector. Preferably, the electron beam detector and the Kossel X-rays detector share a common phosphor element and a common detector. In embodiments, the electron beam receiving surface and the Kossel X-rays receiving surface are switched from one to the other so that one of the receiving surfaces is used depending on which mode is being employed. The device may further include a filter, composed of either an ultrathin beryllium foil or an ultrathin vapor-deposited beryllium film, disposed over the Kossel X-rays receiving surface.
This invention employs the Kossel X-rays reflection method to measure crystal distortion, and crystal orientation of the inner portion of a sample, slightly deeper than the shallow surface, and also employs the electron beam diffraction method to measure crystal orientation of the shallow surface of the sample.
By incorporating the use of both methods, and by incorporating a filter for extracting Kossel X-rays, this invention provides a compact device that can achieve reduced measurement time and enhanced measurement accuracy.